What are the dangers of having multiple rib cartilage harvested from both sides?

Another option is to use cadaveric fresh frozen cartilage to prevent another donor site for you. There are certain surgeons who are very experienced in fusing this type of cartilage and also doing revisions. I would recommend seeing a board-certified plastic surgeon (with a 6 year integrated plastic surgery residency and The Aesthetic Society accredited aesthetic fellowship) for a consultation. I would recommend a physical exam in person to further evaluate what is going on with the nose.

To have rib already harvested from both sides, and then need more, is really unusual. Have you had second and third opinions about what to do, what's needed, what the chances are of significant improvement, what the alternatives are? If you are happy that your doctor is a true expert and he recommends another rib, then if you trust him to perform what sounds like an extremely complicated operation, you should trust his advice on how to get the cartilage that he needs. Acquiring the cartilage is probably much simpler than whatever is planned for your nose. If you're very concerned, ask him about the pros and cons and alternatives (such as banked cartilage) in his hands; he'll probably have good answers.

Cartilage serves to maintain structural integrity in places in the body, especially areas where some flexibility is preferable to rigidity. There are no noted specific complications due to harvesting cartilage per se.
Rib cartilage is one of the more abundant sources for reconstructive purposes.
Best,
Mats Hagstrom MD